Limitation of exercise tolerance in chronic heart failure: Distinct effects of left bundle-branch block and coronary artery disease

OBJECTIVES The aim of this study was to identify resting measurements of left ventricular (LV) function that predict exercise capacity in dilated cardiomyopathy (DCM); in particular, the effects of left bundle branch block (LBBB), coronary artery disease (CAD), and total isovolumic time (t-IVT). BACKGROUND The t-IVT is a major determinant of cardiac output during dobutamine stress in DCM, and is itself determined by the presence or absence of LBBB and CAD. METHODS A total of 111 patients with DCM, 51 with CAD (29 LBBB), and 60 without CAD (30 LBBB) were studied with echocardiography and cardiopulmonary exercise testing. The t-IVT (in s/min) was measured by Doppler echocardiography, and maximal oxygen consumption (peak VO2) and percentage of the normal predicted peak VO2 (%predicted peak VO2) were obtained from exercise testing. RESULTS Left bundle branch block reduced peak VO2 (by 10.5 ml(.)kg(-1)min(-1)) and %predicted peak VO2 (by 33%, both p < 0.001) compared with patients without LBBB. Coronary artery disease reduced peak VO2 (by 5.5 ml(.)kg(-1)min(-1), p < 0.001) and %predicted peak VO2 (by 14%, p < 0.01) compared with those without CAD (p < 0.01). The t-IVT, CAD, LBBB, and QRS duration were univariate predictors of exercise tolerance, but only t-IVT and CAD were independent predictors. The t-IVT at rest correlated with peak VO2 (r = -0.68) and %predicted peak VO2 (r = -0.74, both p < 0.001). The combination of t-IVT and CAD explained 57% (r = 0.75, p < 0.001) of the total variance in exercise capacity. CONCLUSIONS Resting t-IVT and less prominently, CAD, are major determinants of exercise tolerance in DCM. Left bundle branch block significantly determines resting t-IVT and thus peak VO2, Prediction of maximum exercise capacity in DCM is therefore possible from time-domain analysis of LV function at rest. (C) 2004 by the American College of Cardiology Foundation